Screw machine



Nov. 27, 1951 x. F. CASTELLI 2,576,570

SCREW MACHINE Filed Jan. 8, 1946 15 Sheets-Sheet 1 CASTELLI SCREWMACHINE 1s Sheet s 2 Filed Jan. 8 6

Nov. 27, 1951 x. F. CASTELLI SCREW MACHINE 15 Sheets-Sheet 4 Filed Jan;8, 1946 Rwy Nov. 27, 1951 x. F. CASTELLI SCREW MACHINE 15 Sheets-Sheet 5Filed Jan. 8, 1946 x c% Q v I|m mm w s 5:: v R

4 x Q @M a W1 MN 1 Wk WM w R W E 7 z: w a N w =5 A mm mm w W m R 4 i k.Uh a a n NA; G .7 .Q a R a mm w. m N X J K k Q X. F. CASTELLI SCREWMACHINE Nov. 27, 1951 15 Sheets-Sheet 6 Filed Jan. 8, 1946 Nov. 27, 195]I x. F. CASTELLI 2,576,570

SCREW MACHINE rlla lll llli lnununnh Fig-.70

ll? mu I i 11m. M 6 I X. F. CASTELLI SCREW MACHINE Nov. 27, 195] 15Sheets-Sheet 8 Filed Jan 8, 1946 life lid Nov. 27, 1951 x. F. CASTELLISCREW MACHINE l5 Sheets-Sheet 9 Filed Jan. 8, 1946 J 7. n y

NOV. 27, 1951 c s 2,576,570

SCREW MACHINE Filed Jan. 8, 1946 15 Sheets-$heet l0 LE4 HT rum Nov. 27,1951 X. F. CASTELLI SCREW MACHINE Filed Jan. 8, 1946 15 Sheets-Sheet 11Nov. 27, 1951 x. F. CASTELLI 2,576,570

SCREW MACHINE Filed Jan. 8, 1946 15 Sheets-Sheet 12 Nov. 27, 1951 x. F.CASTELLI SCREW MACHINE 15 Sheets-Sheet 13 Filed Jan. 8, 1946 X. F.CASTELLI SCREW MACHINE Nov. 27, 195] 15 Sheets-Sheet 14 Filed Jan. 8,1946 X. F. CASTELLI SCREW MACHINE Nov. 27, 1951 Filed Jan. 8, 1946 15Sheets-Sheet 15 amrbe Patented Nov. 27, 1951 SCREW MACHINE XavierFrancois Castelli, Paris, France, assignor to Societe Cri-Dan, Paris,France Application January 8, 1946, Serial No. 639,773 In France January9, 1945 9 Claims.

The present invention has for its object a screw machine of the typeincluding a succession of operations similar to that of a semi-automaticlathe, i. e. first. cutting, disengagement of the tool, quick backstroke, forward stroke for the next cutting, second cutting, and so onup to completion of the Work, but in which the longitudinal displacementof the tool-holder is controlled by a rotating cam which is moved by thedriving spindle for the work piece, Whereas the progressive transverseadvance of the tool, after each cut, is controlled by another cam alsodriven by such spindle, the various mechanisms being automaticallystopped when the number of cuts selected to perform the screw-cuttinghas been achieved.

In the known machines of this kind, if the succession of operations is,as previously stated, similar to that of a lathe, the dispositionof themovable working parts and of the control parts is however frequentlydifferent from the one whichis in use on the lathes; it is thusnecessary to provide for skilled workers to perform operations for whichsaid machines are designed. On the other hand, with said machines, it isgenerally possible to perform screw-cuttings which are located at alimited distance from the nose of the driving spindle, the mechanismswhich control the longitudinal displacements of the toolholder and thetransverse advance of the tool being mounted on the frame of the machinein close proximity to the spindle and in fixed position with respect tothe latter.

An object of this invention is to provide a screw-cutting machine of thekind above cited, the analogy of which to a lathe being extended, notonly to the succession of operations, but also to the generaldisposition of the frame and of the control and working parts carried bysaid frame, in order to simultaneously profit by the advantages of quickexecution, high yield and accuracy which pertain to the screw-cuttingmachine of the kind referred to.

Another object of this invention is to produce a screw-cuttingmachinewith which it will be possible, not only to performscrew-cuttings on pieces of a great length, but also, as is the casewith a lathe, to localize said screw-cuttings at any points of thelength of said pieces.

Still another object of this invention is to produce a screw-cuttingmachine, in which the mechanisms providing the control of thelongitudinal displacements of the tool-holder, for the control of thetransverse advance of the tool, for the determination of the number ofcuttings and for the automatic stopping, are compactly arranged,entirely located outside and under the working area of the tool-holder,and adequately protected While being easily within reach, so as tocompletely clear said working area and to place the said mechanisms outof reach of collisions and other causes of deteriorations.

/ Still another object of this invention is to produce a screw-cuttingmachine in which the control and adjusting mechanisms above referred toare rationally designed, of a simple construction, easily regulated andof a safe operation.

Other characteristics of the invention will appear from the followingdescription, with reference to the annexed drawings which represent, byway of nonlimitative example, an embodiment of a screw-cutting machineworking with a tool according to this invention, and in which:

Fig. 1 is an elevation of the machine as a whole.

Fig. 2 is an end view.

Fig. 3 is a plan view.

Fig. 4 is a perspective view of the various parts of the machine, viewedfrom the side opposite the worker, the frame, casings and supports.

Fig. 5 is a cross-section of the headstock through V--V of Fig. 1.

Fig. 6 is a longitudinal section through VI--VI of Fig. 5.

Fig. 7 is a longitudinal section of the spindle through VII-VII of Figs.3 and 5.

Fig. 8 is a section of a detail of the control mechanism of the spindle,through VIII-VIII of Fig. 5.

Fig. 9 is an elevation of the set of gears of the headstock and means toreverse the direction of motion.

Fig. 10 is an evolute section through XX of Fig. 9.

Fig. 11 is a cross-section of the carrier through XI-XI of Fig. 1.

Fig. 12 is a longitudinal section through XII-XII of Fig. 11.

Fig. '13 is another cross-section of the carrier through XIII-XIII ofFig. 1.

Fig. 14 is a diagrammatic perspective view of the guiding plate of thelongitudinal carriage.

Fig. 15 is a third cross-section of the carrier through XV-XV of Figure1 and passing through XV-XV of Fig. 14.

Fig. 16 is a longitudinal section of the carrier through XVI-XVI of Fig.15.

Fig. 17 is a fourth longitudinal section of the carrier throughXVII-XVII of Fig. 1.

Fig. 170. is an enlarged sectional view of the control mechanism for thetool holder;

ig. 18 is an end view of the carrier, from the end carrying theback-center.

Fig. 19 is an elevation of the carrier, from the end opposite theworker, the casing which encloses control mechanisms of the tool-holderbeing removed.

Figs. 20 and 21 are two enlarged detail views of the saidmechanisms intwodifierent working positions; 1

- Fig. 22is a section, viewed from above, of another detail, throughXXII-m of Fig. 19.

Fig. 23 is a section of another detail through XXIII-XXIII of Fig. 19.

Fig. 24 is an analogous section of the detail of Fig. 23 in anotherpositionpf'working'. Fig. 25 is a longitudinal section of thebackcenter.

Fig. 26 is an elevation of the back-Fcenter,"

viewed from the side opposite the worker, the

lateral cover being removed.

Figs. 27, 28 and 29 are cross-sections through XXVII+XXVIL XXVIIIXXVIIIand XXIX respectively ofFig; 25.

" The machine showncomprises (Figs. 1, 2 and 3) t ahollow irameconstituted by two 'members i and-2 mounted upon a base 3 and the upperpart i of which constitutes a' work bed with a prismaticslidebar; 'Saidframe encloses a motor 4 connected by a, strap; 5 to theintake' shaft ofa continuous 'change sp'eed device; 6 through which it controls'thefdifferent mechanisms of the machine. On ,the'work bed [are mounted,on; the onehand, a iixedheadstock"! carrying the driving'spindleB'ior'the work piece and, on the other hand, a carrier 9,stationaryduringworking but longitudinal position of which can bevaried; said carrier supports the movable 1 toolholder l and encloses"the'mechanisms adapted .ter. Insaid frame are iastened socket-bearings15-46 (Figs;' 6 and '7) in which the spindleiflijis rotatively mountedthroughball-bearing's such as 11- -18 )(Figi17). The spindle'isconstituted 'by'a tubular element the nose of which carries inwardly aninterchangeable fastening clamp"i9 to" fasten the piece to be screw-cutand; outwardly, a .conicalbutt 2fl to vwhich may be attached, in perfectcoaxial relation, any desired mandrel or mounting. ,Thefa'stening'clanip comprises, at its end'corresponding to the nose ofspindle 8, a conical part lBa to which corresponds a conical-boring 8a iof said spindle. At

rod 2! with which telescopesa'tube 22 of smaller tightening of saidclamp. The opening of the clamp 19 to insert the piece to be screw-cutis accomplished by a thrust exerted in the reverse direction on thecollar 23, by a fork 2'! on which is keyed a lever 28 (Fig. 6)controlled in a manner tobe later described said thrust compress-;ingthe inner-gspring 25 ,and freeingthe conical part 19a of thefastening "clamp.

The rotation of the spindle 8 is effected by means of a pulley 29disposed coaxially of the spindle and connected by V belts 39 with thedrive shaft of the continuous change-speed de- "yi'ce-B (Fig. 1). "Saidpulley 29 is freely mounted 'to automatically control" the, movementsofhthe the inner end of said clamp is screwed a'tubular diameter, thefree end of which protrudes from the spindle} and carriesa collar23screwed on it. On the tube22'is also screwed "asleeve 24 which entersthe spindle 8 'with a lightfriction and on which" bears a-jcompressionspring 25 bearing, at the oth'erend, against a'collar 26 fixed insidethe spindle. Said springjtends thus to push on thesleeve 24andconsequently the tubes 22 and 2lfand the'tastening" clamp 11.9' in thedirection of the arrow; f and so tofo'rc; the

conical part i 9a of the,clampf'against the fconl cal bore 8a ofthespindlfallowirigthusfforthe on the'socket-bearing l5 (Fig. 7) throughanti- ;friction beatings,3 !-32 and so can rotate independentlyof thespindle 8. The pulley 29 is integral with a female clutch cone 33 inwhich can be engaged by a male cone 34 fitted with a'friction band 35and which is a part of a shiftable sleeve' iifi' adapted" to rotate withthe spindle 8 through a ke'y 3land to longitudinally slide on the same.{On the sleeve 36 is mounted, through a hall-bearing- 38, a ring 39on-which is articulated-acontrol'fork '40 (Figs. 5 and 6). On its lowerend, the fork comprisesa hub M through whichit rotates about a shaft l2mountedon the frame"! of the headstock, at rightangles to thegeometrical axis of' the 'spindle ii. The hub '4! is fitted with'alever-43' at the end of -which is provided a housing 43a; in thelatteris' housed a spring'd i-which 'bears, 'at the other end, inanotherhousing :asaprovided in a stirrup-shaped lever 45 adapted to rotateabout'ithe' shaftfd? of the fork. It is through said 1ever14s and thespring 44 acting on the lever 43 of the fork dil that thecones"33"and---34 are brought into engagement in a manner which shall beexplained "meansof a device which comprises a single con- .trol level 49(FigsLl; 4 and 5)'1 mounted on a shaft 501which1rocks' inthe'frame ofthe headstock].

( Saidleverflfidsgnormally maintained in the Vertical position shown'fbythe drawing by means pf a spring 5! fixedQoh the'opehand; to the frame Iof theimachinejthrough an adjustable V V screw "52,v and oni the otherhand ima lever 53. pinned Tonv the shaftT filTlThel shafted carriesaffing'er Q54v positiohedifopposite 'rie, oflthe'farms .55 of. a ldou'blbe: l the .fo

e'ver' lmounted Jon the shaft Z l2 of I mittens the othnlarmss'pfIwhich'is q e'eie regenerat h free end of the lever; is {orig} 6'). Apin as (Fig. 3),

fixed to theiframe of the headstock, sets limits to the angularrnovements ,of. .thefinger..5l. {The lshaftf fl carries also a fingeriiilg dispesed opp osite; one. oflthe arms fi 0 0f a'1- seconddouble,rocK-lever mountedon the-shaft, and on the f other. ar mfl6l oflwhichcar1fies,a I screw $2 by 'mans of ,v'vhic'h -it canegert .a, thrust on,the -s iv upz h sd-l r r A he ou l l v he is integral with an arm 63 adapted to engage an actuating bolt 6}; which fyertically slides in a l'o1"e.. 65 of;theirahie 'i under .the action of a 'knee'. lever; 5,6keyed on ,a shaft I61 adapted to Zrot'at'e' lingthlbbta"fifi and which;ended inside the e' ifi flfl .irh "'68 which, awa t" The control deviceabove described operates as follows (see also Fig. 4).

In order to open the clamp I9 and place in it the piece to be screw-cut,the lever 49 is rocked in the direction of the arrow f1. By suchmovement, the finger 54 bears on the arm 55 of the rock-lever 5556, thearm 58 of which exerts a traction on the rod 51 and then on the lever28. The latter pushes on the collar 23 through the fork 21, thusdetermining the compression of the inner spring 25 of the spindle (Fig.7) and the opening of the clamp I9. The lever 49 being returned to itsvertical position of rest after introduction of the piece into the clampI9, the spring 25 is released and determines by adjustment of the sleeve24 the tightening of the clamp. By a further rocking of the lever 49 inthe direction of the arrow f2 (Figure 4), the finger 59 is caused tobear on the arm 50 of the rock-lever Bil-5|, the other arm BI of which,bearing on the stirrup-shaped lever 45 through the screw 62, compressesthe coupling spring 44 and efiects, by means of the arm 43 and the fork40, the engagement of the cone 34 with the female cone 33 of the pulley29. At the end of said movement, the arm 63 of the lever Bil-6| isclasped on the bolt 64, so maintaining the preceding parts in a positionof engagement.

On its posterior end, the spindle 3 (Fig. 7) carries a pinion 69 throughwhich it transmits its rotation to the mechanisms of the carrier 9. Tothat end, the pinion 89 meshes with a toothed wheel I keyed on a shaftII rotating in ball bearings 12-13 mounted on the frame I of theheadstock. Said shaft 'II carries, on its end located in the casing I3,a pinion I4 which drives a removable outer set of gearsI-'IB--I'I theshafts 'I8'I9 of which are mounted on a support 80 adapted to be lockedin the correct meshing position by means of bolts 8I. Said gears,together with the pinion 14 also removable, determine the step downratio between the speed of rotation of the spindle 8 and the speed ofthe screw-cutting mechanisms carried by the carrier 9. The shaft I9 ofthe last gear 11 carries, inside the frame I of the headstock, a pinion82 adapted to be put into mesh, at will, with one or the other of twopinlons 83-84 mounted on a movable support 85 acting as motion-reversingmeans in order to produce left or right hand threads and which ismaintained in the desired position of rotation by means of locking bolts86. The two inverting pinions 83--84 cooperate with a last pinion 81keyed on a longitudinal shaft 88 which ends inside the carrier 9 whereit controls, as it will be described later, the movements of thescrew-cutting mechanisms. The shaft H connected to the spindle 8carries, on the other hand, inside the headstock I (Figs. 5 and 6), abevel pinion 89 .which controls, through a second pinion 90, atachometer located in a housing 9| fixed on the headstock in front ofthe worker and which allowsfchecking at each instant the speed ofrotation of the spindle.

The carrier 9 (Figs. 11 to 19) consists of a hollow frame fitted, on theone hand, on the prismatic slide-bar Ia of the work bed I, and, on theother hand, on an inclined surface lb of the latter, in order that itcan slide longitudinally on them to modify its position. Saidlongitudinal movement is controlled by means of a pinion 92 meshing witha rack 93 fixed under the prismatic slide-bar Ia (Fig. '11) andtherotation of which is controlled by a hand wheel 94 located on the frontof the machine. After regulation of its longitudinal position, thecarrier can be locked by means of two blocking lugs 9596 bearing undercorresponding rims I0 and Id of the work bed I (Fig. 13) the looking ofwhich is effected through two rods 9I--98 on which act two eccentrics99--I00 mounted on a transverse shaft IOI controlled by a lever I02which is disposed on the front part of the machine.

The carrier 9 comprises at its upper part a rectangular horizontal plateI03 fixed to it by screws I04, and each longitudinal edge of which ischamfered symmetrically at I03a. On the plate I03 is engaged alongitudinal carriage I05 mounted so as to freely slide on the same withthe interposition of four pairs of needle-rollers I06-I0I rolling two bytwo on each of the chamfers I03a (Figs. 14 and 15). The axles l08-I09 ofthe rollers I 06-I0I are respectively mounted on the carriage I05through shoulders I08a-I09a blocked up on said carriage by set screwsIIO. In order to allow for a regulation and taking up of the play, theaxles I09 of the lower rollers I 07 are eccentric with respect to thecorresponding shoulders I09a and the latter is fitted with a groove I09bin which penetrates the corresponding screw IIO; it is thus possible, byrotating the shoulders IBM, to more or less bring the rollers I01 closerfrom the chamfer l03a with which they cooperate.

On the longitudinal carriage I05 is mounted, by means of dovetailedslides III, a movable transverse carriage I I2 on which is mounted,likewise by means of dovetailed slides I I3, a second transversecarriage I I4 carrying the tool-holder turret I0. The displacements ofthe longitudinal carriage I05 on the plate I03 of the carrier,controlled by a mechanism to be described later, correspond to thelongitudinal movements of the tool during the screw-cutting work,whereas the movements of the movable transverse carriage II2 correspondto the movements of transverse feeding and of retraction of the tool. Asfor the upper transverse carriage H4, normally stationary during theworking phase, it is designed to allow adjusting the transverse positionof the tool, said adjustment being obtained through a micrometric screwII5 (Fig. 11) screwed into the movable carriage H2 and the rotation ofwhich is controlled by a milled knob I I 6 and an adjustable vernier IIIcarried by the carriage H4.

The shaft 88 above described, which is set in rotation by the spindle Bthrough the set of gears mounted in the headstock I, ends at the lowerpart of the carrier 9 in which it is carried by ballbearings such asII8I I9 (Fig. 12). Said shaft 88 carries, between the bearings II8I I9,a pinion I20 which is made fast with it for rotation by a key I 2|. Thekey I2I is engaged in a longitudinal groove 88a cut in the shaft 88 andin which it can freely slide, which allows for the pinion I 20 to bemoved along the shaft 88 together with the carrier 9 when thelongitudinal position of the latter is adjusted. The pinion I20 mesheswith a toothed wheel I22 keyed on a shaft I 23 which can rotate inbearings I24-I 25 mounted in the carrier 9 (Figs. 16 and 17). At the endof the shaft I23 opposite the worker is keyed a bell-fashioned cam I 26with the side of which contacts a roller I 21, fixed under thecorresponding end of the longitudinal carriage I05 (see also Fig. 15).The roller I21 is maintained bearing against thacamszlztzby-meanszoritwo'coiripre'ssedr.

springs I 28 disposed :between .the :plate .1 I03 :and:'

thecarriage I05 and which; act to .;urge ithB latter."

be *cutghasa profile which comprises: a first.

helicoidal part which extends, according to'the more or less speedymovement to be obtained. for the tool, byexample-along-an arc ofabout180 oriabout 2&0 and which .-corresponds :to the. working stroke of the.tool; a rectilinear part'causing; stopping of the carriage I05. duringwhich. is. effected the disengagement oi?v the tool and-a: forwardstroke of thesame :havingthe value-:of; the next cutting; and a secondhelicoidal part the obliquity of which is in a. reverse-directionwithrespect to the first one, and which-corresponds to the quick return ofthe .carrage Hi5 under. the action of springs I 28.

In order to allow changing, the cam I26; if necessary, a screw I29-(Fig.13) canlochthe. longitudinal carriage I05 on the carrier. When such achange is to be made, the-machine'is rot-- tated till the roller I2! ison the-upper part of the cam I26,- thenthe carriage Iti-islocked throughthe :screw I29, the cam. I2t-is removed, the-newcamis set-into place,the machine is againeroetated till the lower part: of .thenew cam.-is-=op. posite the roller I2 1, andthescrewI-ZS :is-.1ightlyunscrewed:until said'roller' contacts the-.said'cam;

On the-endof the shaft I23-opposed to that carrying the. cam I26 aremounted twin cams HEM-I362), encased one inthe'oiher, and'fixed. oneplate I3I made fast to the shaft I23ib means of three screwsI32-located-atz120f one from the other; On the circumference-ofsaidcams, which shallbe described'belcw, rollsa roller I33 (Figs. 18 and 19)carriedrbyalever. I34; the lower end of which ismountedon arraxle I35adapted to rotatewith respect to the 'i care rier 9; a-compressed springI 3i-actson .the lever I3.4 to permanently maintain thevroller. I33=incontact withsaid cams. At its upper. end,-.the lever I 34 is connectedbymeans ofa'Gardanjoint I31 to a bar. I38-which 'runsin; a longitudinalslide. I39 providedin-thecarrier 9; the :fTBQFGIld of said-bar is-fittedwith a-slope I3I3a-which:-terminates in apart I 33b of less thickness(Fig. .22) said-part contacting one of the arms of..'a;rocking. leverI40 pivotally mounted on the-carrier by means'of an axle I 44 (Fig. 11). Theother arm of the. lever I49 bears-ona.-pushing rod I42 which isin-contact-with a control elementl43 fixed-on'the transverse carriageI12; said :pusheing rod transmitting to thezcarriage I I2, and-thus to"the tool, the forward transverse motions against theraction ofacompressed spring Iii-42in.- terposed between the. longitudinal.carriage? I05 and-the. transverse carriage I'I*2;and which tendsto-drive the latteraway from the work.

The control-element I43'consistsof a wedge, the. face ofwhich contactsthe pushingnrod-r-MZ being-perfectly plane, which is-pivotally mountedon a vertical .axle I45 fixed to the carriage? H2 .(Figsr-ll, 15,..19and22) The position ofesaid wedge-canbe adjusted :by meansiofftwdscrewsI'AB naSsmsathroueh when 41. proridednnwthe corresponding end of thecarriage H2; thewedge I43 vis.iitted;.witln alateral finger. I43acarrying an index.:;and-...which protrudesout of one edge: 1 of.the-carriagev-IIL. (Figs. 15 and 23) before a. When the.

graduation carried by the latter. wedge I43 is so adjusted that its facecontacte in i'the pushing rod I42 is :parallel to the longitu'dinal.axis ,of .the machine (Fig. 23) the move-.--

ment of-theetool, :during the working phase,. is effectedalonga'trajectory which is parallel to thezsame axis andthere'isobtained a cylindrical screw-cutting; if, ,by means of the screws I46the wedge I43 is obliquelyadjusted with respect to said axis (Fig. 2.4),there is obtained a conical screw-cutting, In ,lieuof theplane wedgeI43,

use may be .made :of a control element of any. desired-profile, toperform. a ,corresponding screwzof cuts and isv laterally closed by acover I52;

pivoted at I52a (Figs. 13 and 15'). The lever E49 (see also .Fig, 20)carries a,pawl I53 which controls. a ratchet wheel I54, the rotation ofwhich in the reverse direction is prevented by a stopping pawl I55;keyedonashaft I55 which is rotatably mounted in anti-frictionbearingsI5'I--I58; carried by the carrier (Fig, 13') a pinion. I59 which meshes:with a. curved rack I60 (Eigs...1l and-12). made'fast' to another shaftIGI rotatably mounted in anti-friction bearings I62-I53. .Attitsendlocated in the casing I5I, theshaft'IS'I carriesa variable-cam I34 ofthe type described in my :co-pendin patent application Serial No.622,166,'filed'onOctober 13, 1945,

(now abandoned) for Process for Controlling on the other hand,- theratio between the depth of the first cuts'andthat of the last cuts. Saidcam I64'acts-on a pushing rod I35, connected by a ball-and socket jointI66 to a sliding bush I31, adjustable in "height, fixed on one arm ofapivotally mounted'lever-llit', the other arm of ;pit ch-.-cam I 26- andwhichicorrespondseto the T tool working phase...theelever .I34..-remains-stationary,

The ratchet wheel I54 is.

the tool being maintained in the same transverse advance position;during the subsequent stopping of the carriage I corresponding to thefirst rectilinear part of the cam I26, the lever I34 is displaced in thedirection of the arrow is (Fig. 19) so as, on the one hand, to bring thethin part I381) of the bar I38 in front of the rocking lever I49 and todetermine, under the action of the spring I44, a transverse movement ofthe carriage II2 towards the worker, thus providing for disengagement ofthe tool, and, on the other hand, to effect, through the rocking of thelever I49, upward movement of the pawl I53 and thus an angular movementof the ratchet wheel I54 of one tooth, which brings, through theintermediary of the pinion I59, the curvedrack I60 and the variable camI64 acting as hereinbefore described, the appropriate movement of thetool at the depth which is necessary for the next cutting operation;during the return stroke of the longitudinal carriage I05 (descendingpart of the cam I26), the lever I34 is moved in the direction of thearrow f4, so as to bring the slope I38a of the bar I 38 to act upon therocking lever I40 and to effect, through the pushing rod I42, theprogressive return of the carriage H2 and thus of the tool in theworking position, said position being reached when the bar I38 presentsits thick part in front of the rocking lever I40. The outline of thetwin cams I 30a-I 30b consequently comprises a plane part extendingalong an arc at least equal to that of the first helicoidal part of thepitch cam I 26; a slope corresponding to the plane part of the cam I26;and a slope inclined in an opposite direction and corresponding to thedescending part of the cam I26. As the first helicoidal part of the camI26 can be extended to 180 or 240, the twin cams I30a-I30b, the outlinesof which are identical, are adapted to be rotated one with respect tothe other over 60 in order to present to the roller I33 of. the lever I34, during the action of said helicoidal part, and as the case will be,a plane part of 180 01' 240. To this end, the cam I 30b is fitted withsix holes I300 spaced 60 from each other (Fig. 18) forming passagewaysfor the three screws 132 connecting it with the cam I29 and the plate I3I.

The angular movement of the variable cam I64, which controls theprogressive depth advance of the tool, is limited to the angle whichcorresponds to the working arc of said cam adapted to determine amovement of advance of the tool according to a positive sinusoidal lawof variation, in correlation with a mechanism which enables determiningat will the number of cuts which the entire advance of the tool mustcomprise. To this end, a spring I69 fixed, at on end, to a screw I fixedto the carrier 9, and, at the other end, to a steel ribbon I'II rolledup round the shaft I 6! of the curved-rack I60, tends to permanentlyreturn the latter backward, said movement being limited by an adjustableabutment I12 provided on the edge of the carrier, Moreover, on one faceof the ratchet wheel I54, is fixed a plate I13 (Fig. 13) carrying a plugI14 which .can be engaged, at will, with one of the holes I15a piercedalong a circumference in a coaxial plate I15, freely mounted on theshaft ,I56, each of said holes corresponding to a predetermined numberof cuts.

The perforated plate I15 carriesa plug I16 on the trajectory of which isdisposed a lever I 11 (Figs. 17 and 19) keyed at the end of a shaft I 18mounted par- 10 allelly to the shaft I56 of the ratchet wheel. on theshaft I18 is keyed a second lever I19 .with two arms, the lower arm ofwhich is located in front of a projection I provided on the stoppingpawl I55. Said lever I19 drawsalong by a claw clutch I19a a third leverI8I mounted on the shaft I18, and the lower arm of which is positionedin front of a projection I82 provided on the pawl I53. The dispositionof said parts is such that, as soon as the plug I16 of the plate I15bears against the lever I11, the levers I19 and I8I respectively arebrought into engagement with the projections'l80 and I82 of the stoppingpawl I55 and pawl I53, raise said two ratchets and clear the ratchetwheel I 54 and the perforated plate i 15. Through the medium of thespring I69, the curved rack I60 is retracted until it is stopped by thestop I12, so returning, through the intermediary of the shaft I6I, thevariable cam I64 to its first original position.

The shaft I18 carrying the levers I19 and I8I for disengaging the pawlI53 and stopping pawl I55, carries also (Fig. 17) an helicoidal pinion I83 meshing with a pinion I84 keyed on the shaft 61, the otherend ofwhich, located inside the headstock 1, carries the lever 66 controllingthe bolt 64 of the clutch. The pinion I84 is made fast for rotation tothe shaft 61 through a key I85 which engages a groove 61a cut into saidshaft and in which it can freely slide, which allows said pinion I84 tobe moved along the shaft 61 together with the carrier 9 when thelongitudinal position of the latter is adjusted. When the shaft I18 isangularly moved by the thrust of the plug I 16 of the perforated plateI15 acting on the lever I11, the shaft 61 is itself rotated by means ofthe pinions I83--I84 and provides, through the lever 66, for theloweringof the bolt 64,.soclearing the lever 63 (Figs. 5 and 6). The latter,urged by a spring I86 adjustable by means of a knob I91, actuates theclutch cone 34 away from the cone 33 of the pulley 29 and engages thebraking cone 46 with the stationary cone48, so automatically stoppingthe rotation of. the. spindle 8 and,. consequently, the working of thewholeof the mechanisms carried by the carrier 9.

Above the shaft I18 is mounted, in the carrier 9, another transverseshaft I81 (Figs. 17 and 19) which extends through the carrier andterminates at the front part of the machine where it carries a controllever I 88 adapted to take three positions and fitted. with a springtensioned detent I89, the opposite end portion being disposed inside thecasing I5I. At the end of said shaft I 81 located inside the casing I5I,is keyed a lever provided with two arms I 90-I 9I arranged in twodifferent planes. The arm I90 is disposed in front of the upper arm ofthe lever I BI so that, when the control lever I88 is rotated in thedirection of the arrow is (Fig. 20), said arm I90 rocks the lever I8Iwhich, acting upon the lug I82 of the pawl I53, moves the latter awayfrom the ratchet wheel I54; the rotation of said latter wheel isthusprevented and the machine runs idle, the tool remaining at the samedepth of out, which allows completing the adjustment of the tool orchecking the work after each cut. The arm I 9I is' disposed in front ofa double lever I92 which, when the control lever I 88 is rotated in thedirection of the ar-

